Photographic processing using cellophane processing sheets



Dec. 17, 1968 J. H. COENEN 3,416,921

PHOTOGRAPHIC PROCESSING USING CELLOPHANE PROCESSING SHEETS Filed Feb. 1. 1965 United States Patent Office Patented Dec. 17, 1968 PHOTOGRAPHIC PROCESSING USING CELLOPHANE PROCESSING SHEETS Joseph H. Coenen, Greece, N.Y., assignor, by mesne assignments, to Minnesota Mining and Manufacturing Company, St. PauL, Minn, a corporation of Delaware Filed Feb. 1, 1965, Ser. No. 429,428 3 Claims. (Cl. 96-29) ABSTRACT OF THE DISCLOSURE A base sheet is coated with a receiving coating of the diffusion transfer type, and over the receiving coating is a negative emulsion coating of the diffusion transfer type, a stripping layer preferably being interposed between the two coatings to facilitate separation of the coatings from each other. After a photographic exposure is made on the negative coating, a sheet of cellophane with processing solution imbibed therein is pressed against the exposed negative coating. The solution develops the latent image in the negative coating, and transfer takes place to the receiving coating (through the intermediate stripping layer, if one is used) to produce a positive image in the receiving coating. The cellophane layer is then stripped off, carrying with it the negative emulsion coating, as the negative coating has greater affinity for the cellophane layer than for the positive or receiving coating. According to another feature of the disclosure, a cellophane sheet may also be used as a vehicle for stripping unwanted gelatin from a photographic element of a type other than a diffusion transfer element.

This invention relates to photographic processing, and more particularly to methods and materials used in developing an image on exposed sensitized photographic material, either negative or positive or both.

An object of the invention is the provision of generally improved and more satisfactory processing techniques, including both methods and materials.

Another object is the provision of improved processing techniques which are useful especially, though not exclusively, in connection with the silver diffusion transfer process.

A further object is the provision of a processing technique in which the processing fluid is absorbed or imbibed in a sheet or web of material which is found to be particularly advantageous and suitable for this purpose and which is also readily available at a modest price.

These and other desirable objects may be attained in the manner disclosed as an illustrative embodiment of the invention in the following description and in the accompanying drawings forming a part hereof, in which the single figure is a schematic cross section through a camera I containing a much enlarged piece of photographic material according to the present invention.

In the well known photographic process often called the silver diffusion transfer process, the photographic exposure is made on a sensitized emulsion of negative character, which is then developed in contact with a receiving sheet or layer which is not light sensitive but which does have nuclei to promote the deposition of silver thereon. Since the basic silver diffusion transfer process and various modifications thereof are well known in the art, it is not necessary here to describe the fundamentals. Details may be found in many standard text books of photography, such as Photography, Its Materials and Processes by C. B. Neblette, fifth edition, published in 1952, pages 234-244. As explained in the book just mentioned, and

as well understood by those experienced in this art, the negative emulsion may be coated on one support and the receiving layer containing the nuclei may be coated on another support, the emulsion and the receiving layer being brought face to face during the transfer step of the process; or, alternatively, the negative layer may be coated over the positive or receiving layer, on the same support. One aspect of the present invention relates particularly to this alternative arrangement, where the negative layer is coated over the positive or receiving layer, in effective functional contact therewith although not necesarily in direct physical contact, for a thin separating layer may be and preferably is interposed between the negative layer and the positive or receiving layer, the thin separating layer being of a character which is permeable and does not prevent the desired transfer of the silver from the negative layer to the receiving layer.

In the past, it has been a common practice to develop the image either by means of a liquid bath, or by means of a viscous or semi-liquid developing material applied between the negative layer and the receiving layer as they are being brought together. The liquid bath technique is not suitable for use in a photographic camera, particularly a small compact hand camera for the amateur. The viscous procesing technique, although often used in amateur cameras, is not wholly satisfactory because it is somewhat messy, and in any event it requires in general that the negative layer and the receiving layer be coated on sepa' rate supports rather than a single support.

The present invention accomplishes development and related steps by a technique which is completely different from that customarily used in the past. According to the present invention, neither a liquid bath of developer nor a mass of viscous developing material is used. On the contrary, the developer is in the form of liquid imbibed or absorbed in a hydrophilic layer or sheet which is brought into contact with the exposed negative layer, allowing enough of the imbibed liquid developer to be transferred to the negative layer to complete the necessary development. -In addition, advantage is taken of the developercarrying hydrophilic layer as a means for removing or stripping the negative layer from the positive layer, leaving the positive layer exposed to view to form the finished print. 1

Referring now to the diagrammatic cross section constituting the single view of the present drawing, there is shown a base layer 11 of any desired photographic base material. Depending upon the ultimate use of which it is to be put, it may be of any desired thickness and any desired stiffness or flexibility. For example, it may be a sheet of glass, or photographic film base, or paper. When exposure and processing are to be accomplished in a small compact hand camera for amateur use, it is most satisfactory to make the base 11 of paper.

Coated on top of this is a receiving layer 13, which may be a conventional receiving layer of any composition known in the diffusion transfer art, containing the desired nuclei.

Over this is a stripping layer 15, likewise well known in the art, to promote or facilitate separation of the receiving layer 13 from the overlying negative emulsion layer 17. All of these layers 11 through 17 are of conventional materials, the details of which are not important for purposes of the present invention, and may be varied within the skill of the art. 7

This composite structure comprising the layers 11, 13, 15, and 17 constitutes the material which is supplied to the camera for exposure purposes, and which is exposed light falling upon the negative layer 17. Then, according to the present invention, the material is fed forwardly out of the focal plane by any suitable conventional feeding means, such as feed rolls or the like, and at the time it leaves the focal plane or at any desired subsequent time, while still in the dark, it is brought into contact with the hydrophilic layer 21 into which the processing fluid has previously been imbibed or absorbed. The hydrophilic layer is pressed firmly against the face of the negative layer 17 by any suitable means; for example, by a guide roller 23 around which the layer 21 travels as it meets the negative structure, pressure being applied in conjunction with a stationary surface or a rotating roller 25 on the opposite face of the composite material, opposite the roller 23.

The pressure means presses the layer 21 against the previous composite layer structure sufficiently firmly so that liquid imbibed in the layer 21 passes from it to the negative layer 17, in sufl'icient quantity to cause development of the negative layer. In the manner well understood in the diffusion transfer art, the undeveloped silver in the negative layer 17 then transfers through the intermediate stripping layer 15 to the receiving layer 13 which contain the nuclei which promote the transfer of the silver, thus forming on the layer 13 a silver image which is a reverse of the latent image in the negative layer 17.

When the transfer is completed from the negative layer 17 to the receiving layer 13, the negative layer 17 should be stripped from the layer 13 in order that the completed positive image on the layer 13 may be exposed to view. This is done by using, as the treating layer 21, a material which has greater aflinity or adhesion for the negative layer 17, than the negative layer has for the receiving layer 13. Hence when the treating layer 21 is pulled or stripped away from the base 11 and receiving layer 13, the negative layer 17 stays with the treating layer 21 and comes with it, away from the receiving layer 13, the separation from the receiving layer being aided by the use of the stripping layer 15 between the layers 17 and 13. The stripping of the layers 21 and 17 away from the receiving layer 13 is shown schematically near the lefthand side of the illustration. This can be done either within the camera or preferably outside of the camera. For instance, the entire composite structure comprising the layers 11 through 21, inclusive, may be pulled or otherwise advanced beyond the pressure means 23, 25, and may be allowed to remain in contact with each other for the required length of time (varying from a few seconds to a minute or more) and then the portion of the composite structure on which the processing has been completed may be torn off from the remaining part of the structure and the layer 21 may be stripped away from the layers 11 and 13, carrying the layer 17 with it. The intermediate stripping layer 15 is so thin in any event that it does not matter whether it comes off with the layer 17 or whether it sticks to the layer 13, or it may remain partly with the positive receiving layer 13 and partly with the negative layer 17.when they are stripped from each other.

The ability of the hydrophilic layer 21 to adhere to the negative layer 17 and pull the negative layer off with it, away from the positive layer 13, is an important feature in a workable structure for processing according to the present technique. When the negative layer and the receiving or positive layer are coated upon separate sheets or supports, the two sheets may be pulled away from each other at the conclusion of processing, in order to remove the negative layer from the positive layer. But this is obviously not possible when the negative layer is coated over the positive layer on a single support, in accordance with the technique to which the present invention relates. When the negative and positive layers are both on a single support, one way to remove the negative layer would be to pass the composite structure through a liquid bath which could dissolve the negative layer without damaging the. underlying positive layer. But this, although theoretically possible, would not be practical in a small compact hand camera for amateur use. The present invention solves the problem by utilizing the special treating layer 21 which serves the double function of, first, forming the vehicle for applying the processing fluid to the negative layer, and second, forming the means or carrier for removing the negative layer from the positive receiving layer when the processing has been completed. The requirements for a special treating layer for performing these two functions are rather severe. It must have enough adhesion for the gelatin in the negative layer 17, to enable it to pull the negative layer with it as the special processing or treating layer is pulled away from the positive layer. In other words, these should be a greater attraction between the hydrophilic treating layer and the photosensitive negative layer, than the attraction between the photosensitive negative layer and the positive receiving layer, at least after the hydrophilic treating layer has been in contact with the photosensitive negative layer for a suflicient length of time to effect development of the negative image and the transfer of the positve image to the receiving layer. In addition to this, the hydrophilic treating layer should be sufiiciently absorbent to be able to hold a quantity of developing solution sufficient to produce the desired results. Also, the special treating layer should have no adverse photographic effects. That is, nothing in the special treating layer should react in an unfavorable way with the photosensitive negative emulsion layer or with any other part or element of the composite photographic structure or of the camera in which it is used. Moreover, the special treating layer should be stable with respect to the alkaline processing fluids or solutions which are to be used. In addition, it would be highly advantageous if this special treating layer were available in the form of a self-supporting film of moderate cost and readily obtainable on the market.

Quite unexpectedly, it has been discovered that all of these desirable characteristics are present in the regenerated cellulose sheeting commonly known as cellophane, and it is the use of cellophane for this purpose which constitutes one of the important features of the present invention. It is preferred to use ordinary cellophane as distinguished from what is called moisture proof cellophane. Ordinary cellophane is well known, and is the subject of many pablished technical articles. See for example the article Cellophane beginning on page 280 of volume 3 (published 1949) of the Encyclopedia of Chemical Technology, edited by Raymond E. Kirk and Donald F. Othmer, published by Interscience, New York City.

Commercial cellophane of the ordinary kind (that is, not moisture proof) having a thickness of 0.002 of an inch, has been found to be very satisfactory for purposes of the present invention. It will readily absorb about 5 milliliters of developer solution per square foot of cellophane. This is enough to produce entirely satisfactory development of the negative and transfer of the image to the positive. This cellophane also has entirely suflicient stability in an alkaline developing solution having a pH value of more than 11.0.

The micro-porous nature of cellophane is also an advantage, in that it permits diffusion of water to the back of the cellophane sheet, to replace the water which evaporates from the back of the sheet, and thus helps in drying the laminated assembly.

The excellent adhesion between the cellophane and the gelation of the photo-sensitive negative emulsion layer was particularly unexpected, and it is this adhesion which is largely responsible for the success of the present invention in enabling a single treating layer (i.e., the cellophane sheet) to serve the double function of a vehicle for applying processing fluid to the composite photographic structure, and a stripping means for stripping the de veloped negative layer from the composite structure.

The discovery of the excellent adhesive characteristics between the cellophane and the gelatin of a photographic emulsion enables the cellophane sheet to be used also, according to another aspect of the invention, in removing gelatin from photographic structures where desired under other circumstances, not necessarily in the practice of the diffusion transfer process. Thus, according to one aspect of the present invention, a sheet of cellophane may be used to adhere to and strip off the unwanted gelatin in connection with any of the well known gelatin relief processes of photography. (See page 422 and following pages of the above cited book by Neblette.)

Preferably but not necessarily, means for holding a supply of the composite photographic material or assembly, and a supply of the cellophane sheeting with processing fluid imbibed therein, are built intoa camera. Thus, as shown very schematically, the camera body 31 may contain means for storing a supply roll 33 of the composite photographic assembly comprising the layers 11, 13, 15 and 17, and means for storing a supply roll 35 of the cellophane material 21 with the fluid imbibed therein. There is means for advancing successive quantities of the photographic material from the supply roll 33 to an exposure position indicated at 41, where the material may be exposed to light coming into the camera through a lens 43, controlled by a suitable shutter (not shown) of known construction. Also there is means for advancing the exposed material from exposure position 41 to what may be termed a processing position or treating position at 47, and simultaneously advancing the desired quantity of cellophane sheeting 21 from the supply 35 to lie in face to face contact with the exposed photographic assembly and more particularly with the negative emulsion layer 17 thereof, during the processing interval and while the negative layer is in the processing position 47. It will be understood that the processing layer or fluid carrying layer 21 of cellophane remains stationary relative to the negative emulsion layer with which it is in contact, during the processing interval. At the conclusion of the processing interval the processed material is cut or torn off of the remaining material and the cellophane layer 21 is stripped away from the support layer 11, the cellophane carrying the negative layer 17 with it and leaving the positive layer 13 behind on the support 11, as already explained above.

When referring to means for advancing the composite photographic assembly or means for advancing the cellophane sheeting 21, this advancing means need be nothing more than a manual pull on the material, to overcome frictional resistance and pull it through between the rollers 23 and 25. Of course power driven feed rollers of known form could be provided, if desired. Also, when referring to means for separating or stripping the cellophane layer 21 from the base or support layer 11, this stripping means again need be nothing more than a manual pull, grasping the base or support layer 11 in one hand and the cellophane layer 21 in the other hand and pulling them apart, away from each other.

At various places in the specification and claims, reference is made to the fact that one layer or coating is in contact with or on another particular layer or coating. It should be understood that these words are used in a functional sense and not as an indication of exact physical construction or relationship, which may be varied. For example, in the preferred construction, the negative layer 17 may be said to be on or carried by the base or support layer 11, even though the layers 13 and 15 are interposed between the layer 17 and the support 11. Again, the negative layer 17 may be said to be in contact wit the positive receiving layer 13, because it is in effective functional contact therewith for transfer of the image from the negative 17 to the positive layer 13, even though the thin stripping layer 15 is physically interposed between them. Likewise, the negative layer 17 may be said to be in contact with the cellophane layer 21 even though it may be desired, at times, to employ a known form of coating over the negative emulsion layer, provided it is of a nature which is permeable and does not interfere with transfer of the imbibed processing fluid from the cellophane layer 21 to the negative emulsion 17 nor interfere with the desired adhesion of the cellophane to the negative emulsion layer.

As stated above, one of the important aspects of the present invention is in the use of a layer of cellophane both as a carrier or vehicle for holding the processing fluid and applying it to the negative emulsion layer, and for the purpose of adhering to the negative emulsion layer to enable the negative layer to be stripped from the positive layer in a quick and easy manner. Therefore, according to the broad aspect of the invention, the exact details of the negative emulsion layer, of the positive or receiving layer, of the stripping layer (if any is used), and of the processing fluid employed, can be varied at will within the skill of the art, and such details are not important to the broad aspect of the invention. However, for the sake of giving a specific example of the invention, it may be said that the following has proven to be satis factory:

The support or base 11 may be of paper of the kind customarily used for photographic prints, such as Baryta paper, having a thickness of about 0.010 of an inch. The positive receiving layer 13 preferably contains nuclei for promoting the transfer of the image from the negative layer. These nuclei may be composed of colloidal particles of silver, gold, or platinum; or of the sulphides, selenides, or tellurides of silver, gold, platinum, or other heavy metals; or of organic mercaptans or metallic salts or organic mercaptans. They may be deposited in gelatin or other colloids or polymers, and they may be adsorbed to colloidal silica, or other inert water-soluble substances that tend to combine the nuclei into suitable aggregates. Suitable receiving layers are well known in the art and are described, for example, in US. Patents 2,352,014, 2,698,236, 2,698,237, 2,698,245, and French Patent 879,995, granted Dec. 10, 1942, and many others.

The negative photosensitive layer 17 is preferably a gelatin-silver halide emulsion layer of conventional known form, having a speed sufficient for instantaneous photography in a popularly priced camera. An emulsion with an ASA exposure index value of ,from to 200 is considered satisfactory.

In order to facilitate the stripping of the negative photosensitive layer 17 from the image receiving layer 13, there may be provided, as already mentioned above, an intervening or stripping layer 15. This layer required or especially desirable only when the photosensitive layer 17 would normally have a greater aflinity from the image receiving layer 13 than for the cellophane processing sheet. This would be the case, for instance, when the image receiving layer 13 contains a large amount of gelatin as a film forming colloid. Suitable stripping layers are known in the photographic art, and can be composed of one or more of the following substances: gum arabic, cellulose acetate, hydrogen phthalate, polyvinyl alcohol, hydroxy ethyl cellulose, methyl cellulose, ethyl cellulose, sodium alginate, pectin, polymethacrylic acid, and other water or alkali soluble polymers. Furthermore, mixtures of the above substances with water soluble non-polymeric substances may also be used. These layers are preferably very thin. It has been found that thicknesses of from one to three microns are effective.

A distinct stripping layer would not be needed in case the aflinity when wet of the photosensitive layer 17 for the receiving layer 13 would be substantially less than its affinity for the cellophane processing sheet. This is the case when the forming colloid of the receiving layer is composed of a material having only limited compatibility for gelatin, such as, for example, polyvinyl alcohol which may be hardened or cross linked such as by means of dimethylurea, or aromatic polyhydroxy compounds.

The processing fluid or solution may be composed of:

Sodium sulphite (anhydrous) grams 40.0 Hydroquinone do 25.0 1-phenyl-3-pyrazolidone do 5.0 Sodium hydroxide do 12.5 Sodium thiosulphate do 20.0 l-phenyl-S-mercapto tetrazole do 0.23 Water to make liter-.. 1.0

Such a solution is absorbed or imbibed into the above mentioned cellophane processing sheet to the extent of about five milliliters per square foot of cellophane.

It is seen from the foregoing disclosure that the objects and purposes of the invention are Well fulfilled. It is to be understood that the foregoing disclosure is given by way of illustrative example only, rather than by way of limitation, and that without departing from the invention, the details may be varied within the scope of the appended claims.

What is claimed is:

1. The method of processing a photographic article which comprises the steps of providing a support layer and a photo-sensitive gelatin layer supported thereby, providing a sheet of cellophane having a greater aflinity for at least part of the gelatin layer than the afiinity between such part of the gelatin layer and the support layer, exposing said gelatin layer to light in the absence of said cellophane sheet, thereafter bringing the cellophane sheet into face to face contact with said gelatin layer, and then stripping the cellophane sheet away from the support layer so that the stripped cellophane sheet carries with it at least some of said gelatin layer.

2. The method of processing a photographic article which comprises the steps of providing a support layer and a photosensitive gelatin layer supported thereby, providing a sheet of cellophane having a greater aflinity for at least part of the gelatin layer than the affinity between such part of the gelatin layer and the support layer, providing a supply of processing fluid imbibed in and carried by said cellophane sheet, exposing said gelatin layer to light in the absence of said cellophane sheet, thereafter bringing the cellophane sheet into face to face contact with said gelatin layer so that fluid imbibed in the cellophane sheet will transfer to said gelatin layer and process said layer, leaving the cellophane sheet in contact with the gelatin layer for a sufficient length of time to complete the processing thereof, and then stripping the cellophane sheet away from the support layer so that the stripped cellophane sheet will carry with it at least some of said gelatin layer.

3. The method of processing a photographic article to produce a silver diffusion transfer image which comprises the steps of:

(a) providing a composite laminated article having (i) a support layer,

(ii) a positive image receiving layer carried by said support layer,

(iii) a negative gelatin layer containing photosensitive silver halide carried by said support layer over said receiving layer, and

(iv) a stripping layer interposed between said receiving layer and said negative layer to facilitate stripping said negative layer away from said receiving layer,

(b) providing a sheet of cellophane (i) having imbibed therein and carried thereby a processing fluid for reacting with silver halide in said negative gelatin layer, and

(ii) having greater afiinity for said negative gelatin layer than the affinity of said negative gelatin layer for the underlying positive receiving layer,

(c) bringing the cellophane sheet into face to face contact with said negative gelatin layer after exposure thereof and maintaining such contact, in stationary position relative to said negative gelatin layer, for suflicient time so that processing fluid imbibed in said cellophane sheet will transfer to said negative gelatin layer and will process the silver halide therein and cause a transfer of silver through said stripping layer to said positive receiving layer, and

(d) then stripping the cellophane sheet away from said support so that the stripped cellophane sheet will carry with it said negative gelatin layer, leaving exposed to view the transferred silver on said positive receiving layer.

References Cited UNITED STATES PATENTS NORMAN G. TORCHIN, Primary Examiner.

R. E. MARTIN, Assistant Examiner.

US. Cl. X.R. 9648 1 

